Recent work has indicated that post-translational modification, particularly acetylation/deacetylation of core histone plays an important role in transcription regulation. However, the mechanism of regulation is not known. The purpose of this proposal is to expand studies towards understanding the mechanism of how histone deacetylation regulate transcription. The focus of this proposal is to expand my on-going studies of the human histone deacetylase containing complexes isolated using antibody against the PAHS domain of the mammalian co-repressor mSin3A. First, I will use a variety of approaches including gel filtration chromatography, affinity chromatography, protein-protein interaction, and yeast genetics to characterize the isolated histone deacetylase containing multiprotein complexes. In addition, I will reconstitute the histone deacetylase containing multiprotein complexes. In addition, I will reconstitute the histone deacetylase enzymatic activity using recombinant histone deacetylase polypeptides. The possible role of the other components of the complex in regulating the histone deacetylase enzymatic activity will also be investigated. Furthermore, I will attempt to reconstitute the transcriptional repression activity of this histone deacetylase complex using chromatin template. Finally, I will analyze the mechanism by which histone deacetylase functions to repress transcription. The proposed studies will help us in understanding how transcription is regulated on the level of chromatin.